The Interior Department and Congress have initiated investigations to determine how a fire started by the National Park Service spread out of control and swept into Los Alamos, N.M., burning hundreds of homes and forcing the evacuation of more than 20,000 residents.

The Park Service Thursday placed on leave the superintendent who took responsibility for the fire.

What was to have been controlled burning by the National Park Service in the Bandelier National Monument to clear underbrush charred a research building at the Los Alamos nuclear laboratory. But Energy Secretary Bill Richardson said all nuclear materials and explosives are located in "fire-resistant buildings," and there was no evidence of radiation leakage.

The federal government may "have to take responsibility" to compensate homeowners for damages caused by the Park Service fire, one official admitted Thursday. The blaze could cost taxpayers millions of dollars in such claims.

Before the fire was ignited on May 4, the National Weather Service in Albuquerque, N.M., sent the Park Service a forecast of high winds, high temperatures and decreased humidity in the area in and around Los Alamos. Such conditions are unfavorable for controlling a fire.

"This seems to be common sense out the window… . We have a terrible situation on our hands," New Mexico Gov. Gary E. Johnson said Thursday as the fire raged out of control and threatened three communities: Los Alamos, the suburb of White Rock and Espanola, located in a valley 10 miles below Los Alamos.

All 11,000 residents of Los Alamos have been evacuated, and another 7,000 in White Rock fled Thursday. About a third of Espanola's 10,000 residents also were asked to leave their homes. There was bumper-to-bumper traffic on evacuation routes from those communities throughout the day.

"Somebody made a mistake. Obviously, we have to find out who. Did someone do something that should not have been done considering the dry conditions and the wind?" asked Sen. Pete V. Domenici, New Mexico Republican, who took part in a high-profile news conference Thursday in Los Alamos. The briefing was broadcast on CNN.

Pressed to identify suspects he blames for the disaster, Mr. Domenici told reporters: "The person responsible for the park service here is most responsible for this."

The senator was referring to the park superintendent, Roy Weaver. According to the Associated Press, Mr. Weaver acknowledged his responsibility for the blaze Monday, saying he believed that conditions were ideal for a "prescribed burn."

Mr. Weaver was put on leave with pay Thursday.

"This action is administrative in nature and in no way reflects on Superintendent Roy Weaver's decisions regarding the fire," said Karen Wade, director of the intermountain regional office of the Park Service.

"Prescribed burn" is the term federal land managers use to describe a fire they set deliberately in an effort to prevent catastrophic wildfires.

The fire ignited by the National Park Service to clear brush quickly flared out of control, beyond its 900-acre perimeter. Racing through ponderosa pine, in 50 mph wind gusts, the blaze consumed 14,000 acres on Wednesday alone.

On Wednesday, when the fire spilled into Los Alamos and began damaging or destroying scores of homes, Mr. Weaver told CNN he never saw the negative weather service forecast.

However, Weather Service supervisory meteorologist Charlie Liles said his staff in Albuquerque faxed the forecast to the park at 12:20 p.m. May 4, before the fire was started. He said his office had received a request for it from Bandelier about an hour earlier. AP obtained a copy of the forecast.

In Washington Thursday, Interior Secretary Bruce Babbitt said his department also would thoroughly investigate the disaster, which he called a "human tragedy."

Mr. Domenici said Thursday the Senate Energy and Natural Resources Committee at his request has asked the General Accounting Office, the investigative arm of Congress, to conduct a probe to determine culpability. "I know we'll know by next week," Mr. Domenici said.

"The controlled burning was started by the National Park Service," Mr. Domenici said. "I'm not sure if the Forest Service was conferred with [about the burning] or if it agreed or disagreed [with the plan] … but you can see it was very risky."

Investigations of the fire will examine the Park Service's plan for the prescribed fire. Each plan includes a description of the area to be burned, a statement about what land managers are trying to accomplish and a set of size and intensity parameters within which the fire will ideally burn.

Interviewed on CNN, Mr. Babbitt was asked if the government would be liable for the 100 homes destroyed in the fire and another 400 or so that were damaged. "Those are things we'll have to deal with," he said.

Shelter and other emergency short-term relief will be provided first, he said. "Then we'll get on to the longer-term issues," said Mr. Babbitt, who planned to fly to New Mexico Thursday night.

Interior spokesman John F. Wright said he assumes the federal government "would have to take responsibility" for compensating for property losses if it is "found liable" for the fire.

Mr. Johnson, the New Mexico governor, sees the potential for mammoth losses. "Right now, there are approximately 100 homes that have burned down. We hope it doesn't get worse. This may just be the beginning of what may be a real tragedy," he said.